1. Field of Invention
The present invention is generally directed to a system for data transfer in an electronic network, and more particularly, to a system for reliably transferring blocks of data in an electronic wireless network.
2. Description of the Related Art
Wired networks focus on managing the queues within routers and assume that the links between routers are either working (99.9% or better packet delivery rate) or failing (0% packet delivery rate). The routers in a wired network work efficiently to process packets with minimum latency, optimize the use of routes for transmission, and anticipate and avoid queue overflows through a variety of mechanisms.
Wireless networks, however, differ substantially from wired networks. Ad-hoc wireless networks with mobile nodes experience packet delivery rates (PDRs) that vary substantially over relatively short time periods. Nodes might be able to communicate with one set of nodes at one moment and then are only able to reach a subset of these nodes a short time later. Wireless networks have substantially lower capacity and the latency for media access control is substantially higher than for the links of high-performance wired routes. These differences substantially alter the landscape for optimal protocol design.
Traditional networking engines place the routing decision primarily at the transmitter. As a router processes packets, the transmitter considers network topology and decides which node is the best choice for the next hop for each packet and then transmits the packet to this specific node. For wireless networks with highly dynamic channels, a choice made according to an approach designed for a wired network may not be the right choice at the time the decision is made. In fact, the communications channels between the nodes can experience a change faster than the node is able to sense. When this occurs, the decisions being made may only be appropriate for a condition that no longer exists.
For example, optimized link state routing protocol (OLSR/OSLR-RFC) with link-quality monitoring is nominally configured with a response time of several seconds. With the HELLO interval set to one second and a measurement window of 10 frames, OLSR computes the link quality over a sliding ten second window based on measurements taken once a second. If a link changes to a 10% PDR for 5 seconds and then recovers, it would take OLSR more than 3 seconds to recognize that the link quality is below 70% PDR and about 10 seconds to realize the full extent of the change in the link's PDR. If OLSR has a threshold set at 70% PDR for causing a change to the OLSR routing table, the change would not be triggered until at least 3 seconds of poor link performance were measured. It would then take OLSR several seconds to propagate this change and start to react. By the time this has all happened, the original example channel disturbance lasting 5 seconds would have already passed.